Day 2

Uroš Godnov

String manipulation

Putting strings together with stringr

str_c()
the c is short for concatentate, a function that works like paste()

[1] "Beautiful day"

[1] NA

[1] "Beautiful NA"

Length

[1] 5 5

[1] 5 5

Error in nchar(f): 'nchar()' requires a character vector

[1] 4 4 8 3

Extracting substrings

str_sub()
extracts parts of strings based on their location
first argument, string, is a vector of strings
the arguments start and end specify the boundaries of the piece to extract in characters
both start and end can be negative integers, in which case, they count from the end of the string

[1] "Bruc" "Wayn"

[1] "uce" "yne"

Matches

str_detect(): answers the question: Does the string contain the pattern?
str_subset(): subsetting strings based on match
str_count(); counting matches

[1] FALSE  TRUE  TRUE

[1] "pepperoni"                 "sausage and green peppers"

[1] 0 1 1

[1] 3 2 5

Parsing strings into variables

str_split(): pull apart raw string data into more useful variables

[[1]]
[1] "23.01.2017" "29.01.2017"

[[2]]
[1] "30.01.2017" "06.02.2017"

Replacing matches in strings

[1] "192" "118" "001"

[1] "510.555.0123" "541.555.0167"

Lab

open names.txt and copy the content
you’ll turn a vector of full names, like “Bruce Wayne”, into abbreviated names like “B. Wayne”. This requires combining str_split(), str_sub() and str_c().
do task using str_split with simplify=TRUE
calculate how many names end with a, h, s and e.

Regular expressions (Advanced)

Why Regular expressions

Most commonly when working with strings
Extracting something from something
Which number is the following string: "10202"?
Is there a number in a string: "102a"? What about in this "1O2"?
We would like to seperate the following string into 3 columns "2,32.1,0.4"!

Regular expressions

syntax to describe patterns
functions on patterns

grep

grep function from base
sub for replacment
stringr package
grep - global regex print. Is there a patern in a string?

string <- "car"
pattern <- "car"
grep(pattern, string)

[1] 1

string <- c("car", "cars", "in a car", "truck", "car's trunk")
pattern <- "car"
grep(pattern, string)

[1] 1 2 3 5

grepl

grepl - returns logical value

string <- c("car", "cars", "in a car", "truck", "car's trunk")
pattern <- "car"
grepl(pattern, string)

[1]  TRUE  TRUE  TRUE FALSE  TRUE

Meta and special characters

special characters: . \ | ( ) [ { ^ $ * + ?
\- escape character
. - any (just one) character
^ - begining of a string
$ - end of string

[1] 1 2 5

[1] 1

[1] 2

Alphanumeric character

[1] 2 3 4

[1] FALSE  TRUE  TRUE  TRUE FALSE FALSE

Non - alphanumeric character

[1] 1 5 6

[1]  TRUE FALSE FALSE FALSE  TRUE  TRUE

Whitespace

[1] 1 6

Non - whitespace

[1] 2 3 4 5

Digit

[1] 3

Non - digit

[1] 1 2 4 5 6

Possible values for a character

using []

[1] 1 2 4

[1] 1 2

All n-characters smallcaps words

[1] 4 7 8

One or two digits anywhere

| - or sign
() - group

[1] 1 2 3 5 6

Exactly one or two digits

[1] 1 2 3

[1] 1 2 3 6

Repeating (1)

repeating operators refer to last character or group
? - matches at most 1 times
* - matches at least 0 times
+ - matches at least 1 times
{m} – matches exactly m times
{m, n} – matches between m and n times
{m, } – matches at least m times

[1] 2 3 4 5 6

[1] 3 4 5 6

Repeating (2)

[1] "ab"  "acb"

[1] "accb"

[1] "accb"   "acccb"  "accccb"

[1] "accb"  "acccb"

All smallcaps letter words

[1] 1 2

Words with letters and length from 3-5

[1] 1 7

Signed numbers

[1] 2 4

Greedy and Lazy Repetition

the repetition operators or quantifiers are greedy
how to make them lazy?
regexpr
regmatches

[1] "<EM>first</EM>"

[1] "<EM>"

gregexpr

finds all positions and lengths of matched patterns

[[1]]
[1] 17 46
attr(,"match.length")
[1] 3 2
attr(,"index.type")
[1] "chars"
attr(,"useBytes")
[1] TRUE

regmatches

extract or replace matched substrings from match data obtained by regexpr, gregexpr or regexec

[[1]]
[1] "100" "45"

Lab

Open regular.txt and complete the excercises

Stringr and regular expressions

str_subset (grep)

 [1] "bell pepper"       "blood orange"      "canary melon"     
 [4] "chili pepper"      "goji berry"        "kiwi fruit"       
 [7] "purple mangosteen" "rock melon"        "salal berry"      
[10] "star fruit"        "ugli fruit"

str_detect (grepl)
str_extract/str_extract_all (gregexpr+regmatches)

[1] "100"

[[1]]
[1] "100" "45"

Text mining (optional)

Data

Why text mining?

85-90 percent of all corporate data is in some kind of unstructured form (e.g., text )
unstructured corporate data is doubling in size every 18 months
text Mining Concepts Benefits of text mining are obvious especially in text rich data environments e.g
law (court orders)
academic research (research articles)
finance (quarterly reports)
medicine (discharge summaries)
marketing (customer comments)
electronic communication records (e.g., Email) Spam filtering Email prioritization and categorization Automatic response generation

Key steps

1. Collection of text document

2. Pre – processing of text

3. Text mining techniques

4. Analyze the text

5. Knowledge discovery

1. Collection of text document

web scraping
scanning and OCR
internal documents

2. Pre – processing of text

tokenization
removal of stop words
stemming

Preprocessing: tokenize and N-grams

N-grams are combination of letters of lenght n in the source text

Tokenize - example

# A tibble: 13 × 2
      id word     
   <int> <chr>    
 1     1 great    
 2     1 white    
 3     1 shark    
 4     1 just     
 5     1 ate      
 6     1 my       
 7     1 leg      
 8     2 not      
 9     2 a        
10     2 wonderful
11     2 day      
12     2 and      
13     2 days

Removal of stop words

the most common words in any language (like articles, prepositions, pronouns, conjunctions, etc)
not adding much information to the text
examples of a few stop words in English are “the”, “a”, “an”, “so”, “what”,…
why removing stop words; removing the low-level information from our text in order to give more focus to the important information
Do we always remove stop words? NO!
Before removing stop words, research a bit about your task and the problem you are trying to solve, and then make your decision!

Removal of stop words

# A tibble: 7 × 2
     id word     
  <int> <chr>    
1     1 white    
2     1 shark    
3     1 ate      
4     1 leg      
5     2 wonderful
6     2 day      
7     2 days

Stemming and lemmatization

Stemming: the process of reducing a word to its stem or root format
Lemmatization: the transformation that uses a dictionary to map a word’s variant back to its root format

Stemming and lemmatization

Stemming and lemmatization - stemming

# A tibble: 13 × 2
      id word  
   <int> <chr> 
 1     1 great 
 2     1 white 
 3     1 shark 
 4     1 just  
 5     1 at    
 6     1 my    
 7     1 leg   
 8     2 not   
 9     2 a     
10     2 wonder
11     2 dai   
12     2 and   
13     2 dai

Stemming and lemmatization - lemmatization

# A tibble: 13 × 2
      id word     
   <int> <chr>    
 1     1 great    
 2     1 white    
 3     1 shark    
 4     1 just     
 5     1 eat      
 6     1 my       
 7     1 leg      
 8     2 not      
 9     2 a        
10     2 wonderful
11     2 day      
12     2 and      
13     2 day

3. Text mining techniques

Concepts

bag of words
NLP

Bag of words

mostly used technique
every word is independent (mostly)
stemming/lemmatization (tourist, tourists and tourism may be the same word)
word frequency
POS
sentiment analysis (different lexicons)
entities extraction
topics identification (e.g. LDA algorithm)

NLP

uses dictionaries to learn (e.g. Stanford NLP)
a subfield of artificial intelligence and computational linguistics. the study of “understanding” the natural human language

Demo

Stanford NLP

Sentiment analysis

lexicons
simple (e.g. Liu&Hu): 1 negative, 0 neutral, +1 positive
advanced (e.g. AFINN): -5<–>+5

How to do it in R - 1

many packages:
- tm, LDA, textmineR, tidyr, sentimentr,…

[[1]]
[1] "The hotel is ideally located and is in a beautiful building."                                                                        
[2] "Most of the staff are very polite and helpful."                                                                                      
[3] "Rooms are comfortable and it has a serviceable gym."                                                                                 
[4] "Avoid going to breakfast before 0700 or wearing flip flops or slippers, you will be admonished and sent back to your room to change."

[[2]]
[1] "The hotel is a short walk to the pedestrian mall, restaurants and cafes."    
[2] "The hotel is an old historical landmark."                                    
[3] "I loved the tall ceilings, lobby and restaurant."                            
[4] "The bathroom has been updated and is very nice."                             
[5] "The breakfast buffet is very good with many options and you can eat outside."
[6] "We enjoyed our stay here."                                                   

attr(,"class")
[1] "get_sentences"           "get_sentences_character"
[3] "list"

How to do it in R - 2

   element_id word_count        sd ave_sentiment
1:          1         52 0.3861717     0.2993681
2:          2         56 0.2501910     0.2914671

   element_id word_count        sd ave_sentiment
1:          1         52 0.1763900    0.14263246
2:          2         56 0.1420433    0.02832483

How to do it in R - 3

   element_id word_count sd ave_sentiment
1:          1          8 NA   -0.03535534

   element_id word_count sd ave_sentiment
1:          1          8 NA   -0.04787702

How to deal with datetime

Creating date/times - 1

the default format for date is yyyy-mm-dd
the default format for time is hh:mm:dd
a date-time is a date plus a time
native class for storing time: hms package

[1] "2019-05-05 18:51:32 CEST"

[1] "2019-05-05 18:51:32 CEST"

[1] "2019-05-05 18:51:32 UTC"

Creating date/times - 2

to get the current date or date-time you can use today() or now() - same as in Excel
from a string, from individual date-time components, from an existing date/time object

[1] "2024-01-17"

[1] "2024-01-17"

[1] "2024-01-17 11:37:35 CET"

[1] "2024-01-17 11:37:35 CET"

From strings - 1

using lubridate

[1] "2017-01-31"

[1] NA

[1] "2017-01-31"

[1] "2018-10-17"

From strings - 2

[1] "2017-01-31 20:11:59 UTC"

[1] "2017-01-31 08:01:00 UTC"

Individual components

make_date()
make_datetime()

[1] "2007-11-05"

[1] "2007-11-05 15:07:00 UTC"

From other types

as_datetime()
as_date()

[1] "2024-01-17 UTC"

[1] "2024-01-17"

Lab

Use the appropriate lubridate function to parse each of the following dates:

Date-time components - 1

[1] 2019

[1] 5

[1] 5

[1] 125

Date-time components - 2

[1] 1

[1] 19

[1] 23

[1] 13

Date-time components - 3

for month() and wday() you can set label = TRUE
abbr = FALSE to return the full name

[1] May
12 Levels: Jan < Feb < Mar < Apr < May < Jun < Jul < Aug < Sep < ... < Dec

[1] Sunday
7 Levels: Sunday < Monday < Tuesday < Wednesday < Thursday < ... < Saturday

Lab

On which day of the week were you born?
On which day of the week will you celebrate 40th birthday?

Durations - 1

when you subtract two dates, you get a difftime object
a difftime class object records a time span of seconds, minutes, hours, days, or weeks
lubridate provides an alternative which always uses seconds: the duration

Time difference of 17660 days

[1] "1525824000s (~48.35 years)"

Durations - 2

[1] "15s"

[1] "600s (~10 minutes)"

[1] "43200s (~12 hours)" "86400s (~1 days)"

Durations - 3

[1] "0s"                "86400s (~1 days)"  "172800s (~2 days)"
[4] "259200s (~3 days)" "345600s (~4 days)" "432000s (~5 days)"

[1] "1814400s (~3 weeks)"

[1] "31557600s (~1 years)"

Periods - 1

periods are time spans but don’t have a fixed length in seconds, instead they work with “human” times, like days and months

[1] "15S"

[1] "10M 0S"

[1] "12H 0M 0S" "24H 0M 0S"

[1] "7d 0H 0M 0S"

Periods - 2

[1] "1m 0d 0H 0M 0S" "2m 0d 0H 0M 0S" "3m 0d 0H 0M 0S" "4m 0d 0H 0M 0S"
[5] "5m 0d 0H 0M 0S" "6m 0d 0H 0M 0S"

[1] "21d 0H 0M 0S"

[1] "1y 0m 0d 0H 0M 0S"

Periods - 3

you can add periods to dates

[1] "2019-10-19 06:00:00 UTC"

Periods - 4

contrive a period to/from a given number of seconds

[1] "1111d 10H 37M 36.0438408851624S"

Lab

import NYCTaxi.xlsx from link
convert pickup_datetime, dropoff_datetime to datetime format (e.g. dataNYC$pickup_datetime<-ymd_hms(dataNYC$pickup_datetime))
calculate the mean duration drive
use seconds_to_period function

As.date - 1

%Y: 4-digit year (1982)
%y: 2-digit year (82)
%m: 2-digit month (01)
%d: 2-digit day of the month (13)
%A: weekday (Wednesday)
%a: abbreviated weekday (Wed)
%B: month (January)
%b: abbreviated month (Jan)

As.date - 2

[1] "2008-09-28"

Locale - 1

change locale

[1] "LC_COLLATE=German_Germany.1252;LC_CTYPE=German_Germany.1252;LC_MONETARY=German_Germany.1252;LC_NUMERIC=C;LC_TIME=German_Germany.1252"

[1] "01-03-18"

[1] "01-Mrz-2018"

[1] "01-März-18"

Locale - 2

[1] "Mrz 01, 2018"

[1] "März 01, 2018"

[1] Donnerstag
7 Levels: Sonntag < Montag < Dienstag < Mittwoch < Donnerstag < ... < Samstag

[1] ""

Lab

Use sys.getlocale and sys.set.locate to:

display today’s month in Checz
display today’s day in Swedish

Lab

In this exercise you will work with the date, “1930-08-30”, Warren Buffett’s birth date! Mind the locale language!

Use as.Date() and an appropriate format to convert “08,30,1930” to a date (it is in the form of “month,day,year”)
Use as.Date() and an appropriate format to convert “Aug 30,1930” to a date
Use as.Date() and an appropriate format to convert “30aug1930” to a date
also solve previous tasks with lubridate functions